抄録
Pt/C catalysts, which were employed for the dehydrogenation of decalin to naphthalene in the liquid-film state under reactive distillation conditions at 483 K, were prepared from the following three procedures; (1) Pt/C with active carbon pretreated with aqueous NaOH solution followed by NaBH4 reduction; (2) Pt/C with the NaOH-pretreated active carbon, followed by H2 reduction; (3) Pt/C with the support but not-pretreated with NaOH followed by NaBH4 reduction. The highest activity for hydrogen-evolution from the dehydrogenation of decalin to naphthalene was observed on Pt/C prepared using the procedure (1). The employment of H2 reduction and the support not-pretreated with NaOH afforded lower activities. The employment of KOH-treatment for NaOH-treatment similarly resulted in the enhancement of the activities, indicating that OH groups but not those alkali metal species directly contributed to the enhancement of the activities. The nearest-neighbor distance of Pt-Pt in the active catalyst, which was estimated with extended X-ray absorption fine structure (EXAFS) analyses, was evidently shorter than those in metallic platinum and in the catalyst prepared from the support not-pretreated with the NaOH solution, while longer than the catalyst prepared from the employment of H2-reduction for NaBH4-reduction. However the distances in those catalysts prepared in the present study were evidently longer than those of Pt2+ and Pt4+. The high dispersion of Pt, which is established with the employment of NaBH4-reduction and the support pretreated with NaOH, affords covalent nature for platinum species, resulting in the highest activities for the dehydrogenation of decalin to naphthalene.
